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NASA NTRS2009

Development of X-Ray Optics for the International X-Ray Observatory (IXO)

The International X-ray Observatory requires mirror assemblies with unprecedented characteristics that cannot be provided by existing optical technologies. In the past several years, the project has supported a vigorous mirror technology development program. This program includes the fabrication of lightweight mirror segments by slumping commercially available thin glass sheets, the support and mounting of these thin mirror segments for accurate metrology, the mounting and attachment of these mirror segments for the purpose of X-ray tests, and development of methods for aligning and integrating these mirror segments into mirror assemblies. This paper describes our efforts and developments in these areas.

Zhang, William W.↗
NASA NTRS2007

Eta Carinae: X-ray Line Variations during the 2003 X-ray Minimum, and the Orbit Orientation

The future evolution of Eta Carinae will be as a supernova (or hypernova) and black hole. The evolution is highly contingent on mass and angular momentum changes and instabilities. The presence of a companion can serve to trigger instabilities and provide pathways for mass and angular momentum exchange loss. X-rays can be used a a key diagnostic tool: x-ray temperatures trace pre-shock wind velocities, periodic x-ray variability traces the orbit, and x-ray line variations traces the flow and orientation of shocked gas. This brief presentation highlights x-ray line variations from the HETG and presents a model of the colliding wind flow.

Corcoran, M. F.↗
NASA NTRS2004

High Resolution Spectroscopy of X-ray Quasars: Searching for the X-ray Absorption from the Warm-Hot Intergalactic Medium

We present a survey of six low to moderate redshift quasars with Chandra and XMM-Newton. The primary goal is to search for the narrow X-ray absorption lines produced by highly ionized metals in the Warm-Hot Intergalactic Medium. All the X-ray spectra can be well fitted by a power law with neutral hydrogen absorption. Only one feature is detected at above 3-sigma level in all the spectra, which is consistent with statistic fluctuation. We discuss the implications in our understanding of the baryon content of the universe. We also discuss the implication of the non-detection of the local (z approx. 0) X-ray absorption.

Fang, Taotao↗
NASA NTRS2007

X-ray Properties of an Unbiased Hard X-ray Detected Sample of AGN

The SWIFT gamma ray observatory's Burst Alert Telescope (BAT) has detected a sample of active galactic nuclei (AGN) based solely on their hard X-ray flux (14-195keV). In this paper, we present for the first time XMM-Newton X-ray spectra for 22 BAT AGXs with no previously analyzed X-ray spectra. If our sources are a representative sample of the BAT AGN, as we claim, our results present for the first time global X-ray properties of an unbiased towards absorption (n(sub H) < 3 x 10(exp 25)/sq cm), local (< z >= 0.03), AGN sample. We find 9/22 low absorption (n(sub H) < 10(exp 23)/sq cm), simple power law model sources, where 4 of these sources have a statistically significant soft component. Among these sources, we find the presence of a warm absorber statistically significant for only one Seyfert 1 source, contrasting with the ASCA results of Reynolds (1997) and George et al. (1998), who find signatures of warm absorption in half or more of their Seyfert 1 samples at similar redshifts. Additionally, the remaining sources (13122) have more complex spectra, well-fit by an absorbed power law at E > 2.0 keV. Five of the complex sources (NGC 612, ESO 362-G018, MRK 417, ESO 506-G027, and NGC 6860) are classified as Compton-thick candidates. Further, we find four more sources (SWIFT J0641.3+3257, SWIFT J0911.2+4533, SWIFT J1200.8+0650, and NGC 4992) with properties consistent with the hidden/buried AGN reported by Ueda et al. (2007). Finally, we include a comparison of the XMM EPIC spectra with available SWIFT X-ray Telescope (XRT) observations. From these comparisons, we find 6/16 sources with varying column densities, 6/16 sources with varying power law indices, and 13/16 sources with varying fluxes, over periods of hours to months. Flux and power law index are correlated for objects where both parameters vary.

Winter, Lisa M.↗
NASA NTRS2016

Reflectivity Around the Gold L-Edges of X-Ray Reflector of the Soft X-Ray Telescope Onboard ASTRO-H

We report the atomic scattering factor in the 11.215.4 keV for the ASTRO-H Soft X-ray Telescope (SXT) obtained in the ground based measurements. The large effective area of the SXT covers above 10 keV. In fact, the flight data show the spectra of the celestical objects in the hard X-ray band. In order to model the area, the reflectivity measurements in the 11.2-15.4 keV band with the energy pitch of 0.4-0.7 eV were made in the synchrotron beamline Spring-8 BL01B1. We obtained atomic scattering factors f1 and f2 by the curve fitting to the reflectivities of our witness sample. The edges associated with the golds L-I, II, and III transitions are identified, of which the depths are found to be roughly 60 percent shallower than those expected from the Henke's atomic scattering factor.

X-rays↗
NASA NTRS2001

Hard X-Ray Lightcurves of High Mass X-Ray Binaries

Using the 7.2 years of continuous data now available from the Burst And Transient Source Experiment (BATSE) aboard CGRO, we have measured orbital periods and produced folded lightcurves for 8 High Mass X-ray Binaries (HMXB). Given the length of the datasets, our determinations are based on many more binary orbits than previous investigations. Thus our source detections have high statistical significance and we are able to follow long-term trends in X-ray output. In particular we focus on two systems: A0538-668 and EXO2030+375 both HMXBs exhibiting Type I outbursts. Recent work on A0538-668 (Alcock et al 1999) reported a 16.65d optical variability due to the orbital period, but only seen during minima of a longer-term variability at 421d. We searched for this signal in the BATSE dataset using an ephemeris derived from Alcock et al ( 1999) & Skinner ( 1982). We found no evidence for such modulation and place an upper limit of 3.0 x 10(exp -3) photon/sq cm.s in the 20-70 keV BATSE energy band , based upon statistical modelling of the signal. EXO2030+375 has exhibited an X-ray active epoch, followed by a quiescent period lasting 2.5yr and since April 1996 has exhibited renewed activity. Previous observations (Reig et a 1998) using RXTE ASM data indicate secondary outbursts occur at apastron passage during the current epoch, but not in the former. We present a lightcurve for the earlier epoch showing convincing evidence for such apastron outbursts. We find apastron outbursts in 3 sources, all having orbital periods greater than 41d. No such signal is conclusively detected in the more rapidly orbiting systems studied.

Laycock, S.↗
NASA NTRS1982

ANS spectrophotometry - The bright X-ray binaries Hercules X-1 /HZ Herculis/ and Cygnus X-1 /HDE 226868/

Complete ultraviolet light curves for HZ Her immediately after a well-defined X-ray turn-on in 1975 are obtained. The features of the curve are found to correspond well with features seen in the optical. The absolute level of emission at maximum light at 1550 A is in good agreement with the calculations of the X-ray reflection effect of Milgrom and Salpeter (1975). It is found that at 1550 A approximately 20% of the light at maximum comes from the accretion disk. Similar observations of Cyg X-1 make it possible to determine the degree of reddening, equivalent to E(B-V) = 0.95 + or - 0.07, from the strength of the 2200 A interstellar absorption feature. The distance inferred from this amount of reddening requires that the optical star be luminous and, therefore, massive. Observations obtained during the May 1975 X-ray transition show ultraviolet excess when compared with the data obtained six months later.

Wu, C.-C.↗
NASA NTRS1986

Modifications of the X-ray source and monitor at the X-ray Calibration Facility

In order to test the instruments aboard the Advanced X-ray Astrophysics Facility (AXAF) some modifications will need to be made in the X-ray Calibration Facility at Marshall. Several of these modifications involve the X-ray source and the monitor. The source was redesigned to increase the spectral purity of the beam and decrease its polarization by minimizing the number of bremsstrahlung photons in the beam. This was accomplished by utilizing an annular electron gun which allowed the beam to take off antiparallel to the direction at which electrons are incident on the anode. Two other features of the source are the conical anode which decreases the effective spot size and a rotatable anode and filter wheel which allow the operator to change targets without breaking vacuum. The monitor is an important part of the facility because it is used to determine the X-ray flux at the target. A commercially available solid-state detector, Si(Li), should be used along with appropriate proportional counters for monitoring. This detector will be particularly useful when energy or wavelength dispersive instruments are tested because of its good resolution.

Newbolt, W. Barlow↗
NASA NTRS1980

Implications of the high-state iron-line feature and soft X-ray emission of Hercules X-1

The interpretation that the soft X-ray emission of Her X-1 is due to reprocessing of the primary hard X-rays intercepted by a plasma layer in the Alfven surface imposes quite a stringent - but not an unreasonable - constraint on its parameters. By using the Alfven shell parameters constrained by this interpretation, the degree of ionization of the Alfven shell is calculated. Because the flux of hard X-ray from the neutron star is greatly attenuated inside the Alfven shell, except for a skin depth from its inner surface, the degree of ionization is determined by photoionization due to soft X-rays produced within the Alfven shell. On one hand, the large soft X-ray luminosity, which is about the same as the hard X-ray luminosity, indicates that a substantial fraction of primary hard X-rays is absorbed by the Alfven shell. On the other hand, the fact that the hard X-ray spectrum of Her X-1 observed during the high state shows neither a significant absorption feature down to about 3 keV nor an iron K-absorption dip tells us that the hard X-rays observed at the earth are mostly not reprocessed. This apparent conflict is resolved if the Alfven shell is clumpy (i.e., made of streams or blobs). The observed iron-line feature around 6.5 keV (E.W. about 300 keV) is explained by fluorescent iron K photons produced as a by-product of reprocessing of the hard X-rays by the Alfven shell; for this a large enhancement of the iron abundance with respect to the solar value is not required.

Bai, T.↗
NASA NTRS1976

Spectroscopic analysis of solar and cosmic X-ray spectra. I - The nature of cosmic X-ray spectra and proposed analytical techniques

X-ray spectroscopic techniques developed in the study of the temperature and density structure of the solar corona are reviewed as introduction to a discussion of the modifications in these techniques which will be required for the study of cosmic X-ray sources. The structure of the interstellar medium - the presence of interstellar grains, the presence of molecules, the ionization structure - are considered in relation to the X-ray opacity of the interstellar medium. The expected spectral structure of individual cosmic X-ray sources is reviewed with emphasis on galactic supernova remnants and galactic binary X-ray sources.

Walker, A. B. C., Jr.↗
NASA NTRS2007

A Stellar-mass Black Hole in the Ultra-luminous X-ray Source M82 X-1

We have analyzed the archival XMM-Newton data of the archetypal Ultra-Luminous X-ray Source (ULX) M82 X-1 with an LO5 ksec exposure when the source was in the steady state. Thanks to the high photon statistics from the large effective area and long exposure, we were able to discriminate different X-ray continuum spectral models. Neither the standard accretion disk model (where the radial dependency of the disk effective temperature is T(r) proportional to r(sup -3/4)) nor a power-law model gives a satisfactory fit. In fact, observed curvature of the M82 X-1 spectrum was just between those of the two models. When the exponent of the radial dependence (p in T(r) proportional to r(sup -P)) of the disk temperature is allowed to be free, we obtained p = 0.61 (sup +0.03)(sub -0.02). Such a reduction of p from the standard value 3/4 under extremely high mass accretion rates is predicted from the accretion disk theory as a consequence of the radial energy advection. Thus, the accretion disk in M82 X-1 is considered to be in the Slim disk state, where an optically thick Advection Dominant Accretion Flow (ADAF) is taking place. We have applied a theoretical slim disk spectral model to M82 X-1, and estimated the black hole mass approximately equal to 19 - 32 solar mass. We conclude that M82 X-1 is a stellar black hole which has been produced through evolution of an extremely massive star, shining at a several times the super-Eddington luminosity.

Okajima, Takashi↗
NASA NTRS1986

X-ray-selected M dwarfs and the diffuse X-ray background

A systematic optical identification program was carried out for serendipitous X-ray sources discovered by the Einstein Observatory. A total of 104 were detected above the threshold flux of 3 x 10 to the -13th ergs/sq cm per sec in the 114 sq deg survey region; 11 of these 104 sources are dM stars. Including X-ray-selected M dwarfs from the LMC survey, the Medium Sensitivity Survey, and the Einstein Deep Survey, a dwarf M star composite X-ray spectrum was constructed; the best-fit thermal model yields kT = 1.3 + or - 0.3 keV, consistent with typical active star spectra. An M dwarf X-ray luminosity function was also constructed and it is concluded that the integrated contribution to the diffuse soft (0.28-1.0 keV) X-ray background from such stars is less than 10 percent, a factor of more than about 2 lower than previous estimates. This result is consistent with a limit on the dwarf M star contribution derived from a spectral decomposition of the observed X-ray background spectrum.

Caillault, J.-P.↗
NASA NTRS1993

Optical and X-ray observations of the low-mass X-ray binary EXO 0748-676

Optical and X-ray observations of EXO-676 in late March 1989 are presented. Our optical observations provide some support for the previously observed correlation between the mean optical brightness and light curve morphology. Unexpectedly, the mean X-ray and optical flux levels during this period do not reflect similar system states. The optical counterpart is found to be in an intermediate to low state, while X-ray data imply a bright (high) state. The changed relationship between optical and X-ray fluxes is evidence showing that EXO 0748-676 has possibly evolved. We fail to find correlated variability in simultaneous X-ray and optical observations. The lack of covariability is attributed to the limited simultaneous coverage of the source and/or significant geometric modulation in the optical light curve.

Thomas, Brian↗
NASA NTRS2000

X-Ray Line Spectroscopy of Massive X-Ray Binaries

Spectra from ASCA have provided the most, detailed view to date of the X-ray spectral properties of stellar winds in massive X-ray binaries. Using detailed atomic models that account for recombination cascade kinetics, we have reexamined archival data from Vela X-1 and Cen X-3 in the context of simple models of their wind geometries and velocity distributions. Our approach emphasizes apparent differential emission measure (DEM) distributions, and their dependence on orbital phase and wind parameters. A grid of theoretical DEM distributions is used to generate model spectra, which are compared to the data. We obtain good fits, and derive constraints oil the stellar wind parameters. We provide a summary of the method, and show that, even though the companion stars in Vela X-1 and Cen X-3 have comparable mass-loss rates, the winds in these two systems are dramatically different, in character.

Liedahl, D. A.↗
NASA NTRS1979

Detection of soft X-ray emission from SMC X-1

The observation of 0.25-keV X-rays from SMC X-1 by a soft X-ray experiment aboard OSO 8 is reported. The variable soft X-ray source observed is identified with the hard X-ray source SMC X-1 on the basis of a rather abrupt ending to the emission (fall time about 2.5 hr) at the time SMC X-1 was expected to enter eclipse. A source luminosity of about 5 x 10 to the 38th erg/s in the 0.18-0.28-keV range is derived by assuming a distance of 68 kpc and correcting for attenuation by 3.4 x 10 to the 20th H atoms per sq cm of intervening galactic gas; this luminosity is shown to be about a factor of 40 greater than the observed coincident luminosity in the 0.8-3-keV band. The soft X-ray intensity upon emergence from eclipse is found to be reduced by a factor of at least 20 from the peak intensity prior to eclipse. It is suggested that this asymmetry may reflect a geometry in which the soft X-ray source trails the compact star as in an accretion-stream model.

Bunner, A. N.↗
NASA NTRS2008

Chandra X-ray Grating Spectrometry of Eta Carinae near X-ray Minimum: I. Variability of the Sulfur and Silicon Emission Lines

We report on variations in important X-ray emission lines in a series of Chandra grating spectra of the supermassive colliding wind binary star eta Car, including key phases around the X-ray minimum/periastron passage in 2003.5. The X-rays arise from the collision of the slow, dense wind of eta Car with the fast, low-density wind of an otherwise hidden companion star. The X-ray emission lines provide the only direct measure of the flow dynamics of the companion's wind along the wind-wind collision zone. We concentrate here on the silicon and sulfur lines, which are the strongest and best resolved lines in the X-ray spectra. Most of the line profiles can be adequately fit with symmetric Gaussians with little significant skewness. Both the silicon and sulfur lines show significant velocity shifts and correlated increases in line widths through the observations. The R = forbidden-to-intercombination ratio from the Si XIII and S XV triplets is near or above the low-density limit in all observations, suggesting that the line-forming region is > 1.6 stellar radii from the companion star, and that the emitting plasma may be in a non-equilibrium state. We show that simple geometrical models cannot simultaneously fit both the observed centroid variations and changes in line width as a function of phase. We show that the observed profiles can be fitted with synthetic profiles with a reasonable model of the emissivity along the wind-wind collision boundary. We use this analysis to help constrain the line formation region as a function of orbital phase, and the orbital geometry. Subject headings: X-rays: stars -stars: early-type-stars: individual (q Car)

Henley, D. B.↗